It is known from the state of the art that mesityl oxide can be reversed into acetone from which it is formed by treatment under acidic or basic conditions. For example, U.S. Pat. No. 2,351,352 discloses a process for producing isophorone by condensing acetone whereas mesityl oxide which is formed inter alia as a by-product during this reaction is reversed into acetone by commingling the crude product mixture with aqueous sodium hydroxide solution, followed by distilling the thus obtained acetone in one step together with unreacted acetone from the main reaction. This prevents forming further mesityl oxide in case of a preliminary removal of unreacted acetone.
The manufacture of phenol and acetone which is of great economic importance typically proceeds starting from cumene according to the Hock reaction by acid catalyzed cleavage of cumene hydroperoxide. The by-products formed during this reaction, like for example, cumene, benzene and one or more ketones, have to be separated from the main products phenol and acetone, which generally proceeds via extraction and/or distillation.
Often an acetone stream obtained from a preceding distillation to separate it from phenol, is treated with alkaline reagents to further separate it from undesired byproducts, especially aldehydes. Because of these acidic and alkaline reaction conditions, respectively, the acetone partly reacts with itself to form diacetone alcohol in a first step which may either dehydrate to form mesityl oxide or decompose again to redevelop acetone.
Since acetone represents one of the desired products a procedure in which the crude product of the Hock process is directly commingled with an alkaline solution to reverse mesityl oxide contained therein to acetone analogous to U.S. Pat. No. 2,351,352 as mentioned above, is not suitable in this case because under these conditions additional byproducts would be formed which leads to a reduction in yield. Moreover, any further acetone purification steps using an alkaline solution also will result in the production of mesityl oxide which accordingly would not be recovered and therefore as well lead to an additional loss of yield.
Accordingly, EP-A-1 188 737 discloses a process for the work-up of substance streams containing mesityl oxide which are especially obtained from acetone purification during the Hock process.
In this process the mesityl oxide is concentrated and reversed to acetone using an acidic or basic aqueous medium or an acidic catalyst in the presence of water.
The disadvantages of this recovery process for mesityl oxide can be seen in the cleavage taking place in a separate reaction apparatus which increases the costs for new plants to be constructed, as well as the costs for the maintenance of such a plant. Additionally, the only process exemplified therein represents a discontinuous one which is susceptible for disorders.
Abstract of JP-A 79 70,210 also deals with acetone recovery from mesityl oxide in the cumene process of phenol manufacture whereas in this process the alkali required for the conversion is a waste liquor from the acetone purification in the cumene processes. Since the cleavage of mesityl oxide described therein proceeds in an autoclave this process as well requires a separate reaction apparatus.
Accordingly the problem underlying the present invention presents as providing a process for recovering acetone from a waste stream from an acetone purification stage which requires less apparative expenses and preferably reduces maintenance costs as well.